function EventEmitter() {
    this._events = this._events || {};
    this._maxListeners = this._maxListeners || undefined;
}

// Backwards-compat with node 0.10.x
EventEmitter.EventEmitter = EventEmitter;

EventEmitter.prototype._events = undefined;
EventEmitter.prototype._maxListeners = undefined;

// By default EventEmitters will print a warning if more than 10 listeners are
// added to it. This is a useful default which helps finding memory leaks.
EventEmitter.defaultMaxListeners = 10;

// Obviously not all Emitters should be limited to 10. This function allows
// that to be increased. Set to zero for unlimited.
EventEmitter.prototype.setMaxListeners = function(n) {
    if (!isNumber(n) || n < 0 || isNaN(n))
        throw TypeError('n must be a positive number');
    this._maxListeners = n;
    return this;
};

EventEmitter.prototype.emit = function(type) {
    var er, handler, len, args, i, listeners;

    if (!this._events)
        this._events = {};

    // If there is no 'error' event listener then throw.
    if (type === 'error') {
        if (!this._events.error ||
            (isObject(this._events.error) && !this._events.error.length)) {
            er = arguments[1];
            if (er instanceof Error) {
                throw er; // Unhandled 'error' event
            }
            throw TypeError('Uncaught, unspecified "error" event.');
        }
    }

    handler = this._events[type];

    if (isUndefined(handler))
        return false;

    if (isFunction(handler)) {
        switch (arguments.length) {
            // fast cases
            case 1:
                handler.call(this);
                break;
            case 2:
                handler.call(this, arguments[1]);
                break;
            case 3:
                handler.call(this, arguments[1], arguments[2]);
                break;
            // slower
            default:
                args = Array.prototype.slice.call(arguments, 1);
                handler.apply(this, args);
        }
    } else if (isObject(handler)) {
        args = Array.prototype.slice.call(arguments, 1);
        listeners = handler.slice();
        len = listeners.length;
        for (i = 0; i < len; i++)
            listeners[i].apply(this, args);
    }

    return true;
};

EventEmitter.prototype.addListener = function(type, listener) {
    var m;

    if (!isFunction(listener))
        throw TypeError('listener must be a function');

    if (!this._events)
        this._events = {};

    // To avoid recursion in the case that type === "newListener"! Before
    // adding it to the listeners, first emit "newListener".
    if (this._events.newListener)
        this.emit('newListener', type,
            isFunction(listener.listener) ?
                listener.listener : listener);

    if (!this._events[type])
    // Optimize the case of one listener. Don't need the extra array object.
        this._events[type] = listener;
    else if (isObject(this._events[type]))
    // If we've already got an array, just append.
        this._events[type].push(listener);
    else
    // Adding the second element, need to change to array.
        this._events[type] = [this._events[type], listener];

    // Check for listener leak
    if (isObject(this._events[type]) && !this._events[type].warned) {
        if (!isUndefined(this._maxListeners)) {
            m = this._maxListeners;
        } else {
            m = EventEmitter.defaultMaxListeners;
        }

        if (m && m > 0 && this._events[type].length > m) {
            this._events[type].warned = true;
            console.error('(node) warning: possible EventEmitter memory ' +
                'leak detected. %d listeners added. ' +
                'Use emitter.setMaxListeners() to increase limit.',
                this._events[type].length);
            if (typeof console.trace === 'function') {
                // not supported in IE 10
                console.trace();
            }
        }
    }

    return this;
};

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

EventEmitter.prototype.once = function(type, listener) {
    if (!isFunction(listener))
        throw TypeError('listener must be a function');

    var fired = false;

    function g() {
        this.removeListener(type, g);

        if (!fired) {
            fired = true;
            listener.apply(this, arguments);
        }
    }

    g.listener = listener;
    this.on(type, g);

    return this;
};

// emits a 'removeListener' event iff the listener was removed
EventEmitter.prototype.removeListener = function(type, listener) {
    var list, position, length, i;

    if (!isFunction(listener))
        throw TypeError('listener must be a function');

    if (!this._events || !this._events[type])
        return this;

    list = this._events[type];
    length = list.length;
    position = -1;

    if (list === listener ||
        (isFunction(list.listener) && list.listener === listener)) {
        delete this._events[type];
        if (this._events.removeListener)
            this.emit('removeListener', type, listener);

    } else if (isObject(list)) {
        for (i = length; i-- > 0;) {
            if (list[i] === listener ||
                (list[i].listener && list[i].listener === listener)) {
                position = i;
                break;
            }
        }

        if (position < 0)
            return this;

        if (list.length === 1) {
            list.length = 0;
            delete this._events[type];
        } else {
            list.splice(position, 1);
        }

        if (this._events.removeListener)
            this.emit('removeListener', type, listener);
    }

    return this;
};

EventEmitter.prototype.removeAllListeners = function(type) {
    var key, listeners;

    if (!this._events)
        return this;

    // not listening for removeListener, no need to emit
    if (!this._events.removeListener) {
        if (arguments.length === 0)
            this._events = {};
        else if (this._events[type])
            delete this._events[type];
        return this;
    }

    // emit removeListener for all listeners on all events
    if (arguments.length === 0) {
        for (key in this._events) {
            if (key === 'removeListener') continue;
            this.removeAllListeners(key);
        }
        this.removeAllListeners('removeListener');
        this._events = {};
        return this;
    }

    listeners = this._events[type];

    if (isFunction(listeners)) {
        this.removeListener(type, listeners);
    } else if (listeners) {
        // LIFO order
        while (listeners.length)
            this.removeListener(type, listeners[listeners.length - 1]);
    }
    delete this._events[type];

    return this;
};

EventEmitter.prototype.listeners = function(type) {
    var ret;
    if (!this._events || !this._events[type])
        ret = [];
    else if (isFunction(this._events[type]))
        ret = [this._events[type]];
    else
        ret = this._events[type].slice();
    return ret;
};

EventEmitter.prototype.listenerCount = function(type) {
    if (this._events) {
        var evlistener = this._events[type];

        if (isFunction(evlistener))
            return 1;
        else if (evlistener)
            return evlistener.length;
    }
    return 0;
};

EventEmitter.listenerCount = function(emitter, type) {
    return emitter.listenerCount(type);
};

function isFunction(arg) {
    return typeof arg === 'function';
}

function isNumber(arg) {
    return typeof arg === 'number';
}

function isObject(arg) {
    return typeof arg === 'object' && arg !== null;
}

function isUndefined(arg) {
    return arg === void 0;
}